Web Science Stream

Web Science Stream Models, Views and Controllers

Case Study: digg

Creating our shovell application rails shovell

Generating our model • To generate a new data model for our application we’ll use the comand below • Our Story model will get two attributes • Name • Link • String is a type which holds up to 255 alphanumeric characters • cd shovell • ruby script/generate model Story name:string link:string

The output should be ... • exists app/models/ • exists test/unit/ • exists test/fixtures/ • create app/models/story.rb • create test/unit/story_test.rb • create test/fixtures/stories.yml • create db/migrate • createdb/migrate/20091019052909_create_stories.rb

Let’s look at the output • story.rb • In the app/model • Creates a blank ActiveRecord • story_test.rb • Automatically generated unit testing • stories.yml • Helps our unit testing and is called a Fixture • Fixtures are files containing simple data for unit testing purposes • 20091019052909_create_stories.rb • A migration file

YAML • Lightweight format to represent data • Has the .yml extension • Have a look at the test/fixtures/stories.yml

stories.yml • # Read about fixtures at http://ar.rubyonrails.org/classes/Fixtures.html • one: • name: MyString • link: MyString • two: • name: MyString • link: MyString

stories.yml • # Read about fixtures at http://ar.rubyonrails.org/classes/Fixtures.html • one: • name: My web site • link: http://abc.net • two: • name: Other web site • link: http://www.theotherwebsite.com

I’m going to Migrate! • Migration files • Used to make modifications to the database schema • All through Ruby code • No SQL needed • Files are numbered so they can be executed sequentially • They are executed in order • Located in the db/migrate dir

20091019052909_create_stories.rb • class CreateStories < ActiveRecord::Migration • def self.up • create_table :stories do |t| • t.string :name • t.string :link • t.timestamps • end • end • def self.down • drop_table :stories • end • end

Let’s do a small modification • Change • create_table :stories do |t| • To • create_table :stories, :force =>true do |t| • Useful if we already have some table structures defined in the database

Let’s make our migrate • rake is based upon the C make tool • Very versatile and allows us to do a number of things ... • Try • rake –T • In our example we’ll make the migration by invoking • rake db:migrate

rake db:migrate • Checks the database for the most recent migration • Steps through the migrations that have not been applied • For each migration execute the up method

The output == CreateStories: migrating ================== -- create_table(:stories) -> 0.0040s == CreateStories: migrated (0.0050s) ========= • If it is successful we will find a stories table in our shovell database

Rolling back • rake db:migrate version=n • Eg: undo all the tables in the database by invoking: • rake db:migrate version=0

Playing with the data • Open a rails console • ruby script/console

Creating our first record • s = Story.new • s.name = “My new website” • s.link = “http://abc.net” • s.save • The end result should be • => true

More on records ... • To see the record id • s.id • To check if its a new record • s.new_record? • To check the number of Stories in the DB • Story.count • Another way of creating records • Story.create( :name => ‘Abc’, :link => ‘http://www.mysite2.com’)

Retrieving records • Story.find(2) • Story.find(:all) • Story.find(:all).last • Story.find(:first, :order => ‘id DESC’)

Dynamic finders ... • Story.find_by_name(‘Abc’) • How would we find the link ‘http://abc.net’? • Try it ...

Let’s update • s = Story.find_by_name(‘Abc’) • s.name = ‘Abcd’ • s.save

Let’s update and save in just one step • s = Story.find_by_name(‘Abcd’) • s.update_attribute :name. ‘Abcde’

Bye Bye records • s.destroy • Try to find the record ... what’s the message?

What about SQL? • Have a look at • log/development.log • CREATE TABLE "stories" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "name" varchar(255), "link" varchar(255), "created_at" datetime, "updated_at" datetime

Generating our first controller! • ruby script/generate controller Stories index

The output • exists app/controllers/ • exists app/helpers/ • create app/views/stories • exists test/functional/ • create test/unit/helpers/ • create app/controllers/stories_controller.rb • create test/functional/stories_controller_test.rb • create app/helpers/stories_helper.rb • create test/unit/helpers/stories_helper_test.rb • create app/views/stories/index.html.erb

Explaining the output • First it generates a number of folders (unless they have been created already) • StoriesController • Has defined the index method • stories_controller_test.rb • Will hold the test functions • stories_helper.rb • Class to help the controller • Index.html.erb • One of the views which will be our initial template

Let’s see what we have so far ... • Start a server • ruby script/server • Goto • http://127.0.0.1:3000/stories

Creating views Two ways ... With or Without scaffolding!

What is scaffolding? • A powerful feature of rails • Quickly creates a web interface for interacting with your model • Provides an easy way to add, manipulate and delete records • Scaffold generates a model, controller, actions and other templates

Limitations of Scaffold • Designed for quick interaction only • Not intended as a fully automateed web site generator • It can’t cope with associations (relationships) between objects

Let’s scaffold! • ruby script/generate scaffold Story name:String link:String

Script/generate • Scaffold is essentially a script that we invoke using script/generate • The nice thing about script/generate is that there exists a script/destroy using exactly the same arguments • So let’s destroy the scaffold • ruby script/destroy scaffold Story name:String link:String

Ohh No!! We lost everything!! • ruby script/generate model Story name:stringlink:string • ruby script/generate controller Stories index

Views • app/views/stories • Only index.html.erb so far • Generated as a static page • Let’s add some dynamic information • Insert • <%= Time.now %>

Problems! • We shouldn’t be including ruby code directly in the view • Ideally we keep them separated so ... • In the /app/controllers/stories_controller.rb • In the def index add • @current_time = Time.now • In the app/views/stories/index.html.erb replace the previous code with • <%= @current_time %> • Try it out!

Let’s do something more useful • In the controller /app/controllers/stories_controller.rb • In the def index, remove what we just wrote and write • @story = Story.find(:first, :order => ‘RANDOM()’) • In the app/views/stories/index.html.erb replace the previous code with • A random link: <%= link_to @story.name, @story.link %>

Didn’t work? • Why not add some data and try again? • ruby script/console • Loading development environment (Rails 2.3.2) • >> s = Story.new • >> s.name = "ABC" • >> s.link = "http://aaa.com" • >> s.save

Questions?

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